At her mother's dying request, in order to carry on her father's insurmountable vendetta against Daigo, the child takes on a man's identity and grows up without a permanent home or any friends.

He only survives because he is discovered by a master spellcaster, who takes pity on him and replaces his missing body parts with those of deceased children.

Killing a pair of dog demons who tormented him about this revelation, Hyakkimaru gains his real eyes and is later confronted at daybreak by Tahōmaru, the man he learned to be his younger brother.

Once dead, Hyakkimaru regained his heart, yet complained that the pain in his chest did not subside afterward, an indication that he was feeling remorse for the first time in his life.

Though later offered the throne, Hyakkimaru declines and entrusts his younger brother with it as he and Dororo continue their quest to kill the remaining two dozen demons.